1. Field of the Invention
The present invention relates to a water purifier and water purification method, to which a forward osmosis process using an aqueous solution containing a volatile solute and a polymer is applied.
2. Description of the Related Art
A reverse osmosis (RO) process, which uses external pressures, and a forward osmosis (FO) process have been known as methods for selectively separating and transporting water between two aqueous solutions having mutually different osmotic pressures.
One example of the forward osmosis processes is a method using a volatile ion-containing aqueous solution including volatile anions and volatile cations. For example, there is a proposal of a water purifying device such that the device contains: a diluting unit 11 configured to bring targeted water for purification into contact with a volatile ion-containing aqueous solution including volatile anions and volatile cations through a semi-permeable membrane 1, and to dilute the volatile ion-containing aqueous solution with the water separated from the targeted water by the semi-permeable membrane 1; a separating unit 15 containing a distillation column 7 configured to make the volatile anions and the volatile cations volatilize from the diluted volatile ion-containing aqueous solution by the diluting unit; and a dissolution unit 14 containing a gas absorption unit 6 configured to return and dissolve the vaporized anion and cation gases separated by the separating unit 15 to and in the diluted volatile ion-containing aqueous solution, as shown in FIG. 1 (see US Patent Application Publication No. 2005/0145568).
However, the proposed water purifying device shown in FIG. 1 has a problem such that non-polar gas components (e.g., carbon dioxide, carbonic acid that is hydrate of carbon dioxide, and ammonium) may non-selectively leak into targeted water across a semi-permeable membrane 1 when the targeted water is brought into contact with the volatile ion-containing aqueous solution, in which volatile anions and volatile cations are contained, through the semi-permeable membrane 1. Since carbon dioxide, carbonic acid that is hydrate of carbon dioxide, ammonium, and the like have the similar physical properties (e.g. molecular sizes) to those of water, it is very difficult to prevent these components from passing through the semi-permeable membrane 1, which selectively passes water through. For example, in the case where a forward osmosis permeable membrane of Hydration Technology Innovations (commercial product) is used as the semi-permeable membrane 1 in the proposed water purifying device, it has been known from the experiment that the gas is components, such as carbon dioxide, hydrate thereof (carbonic acid), and ammonium, leak at the rate of a few to several moles per square meter per hour.
If leakage is occurred at such rate, the targeted water, which will be discharged, may end up containing a large amount of carbon dioxide, hydrate thereof (carbonic acid), ammonium or the like. This adversely affects the recovering system of the water purifying device. Specifically, recycling cannot be carried out unless a large amount of an osmotic source, such as carbon dioxide or ammonium, is resupplied to the volatile ion-containing aqueous solution. For this reason, water purification cannot be performed efficiently. Since the targeted water to be discharged contains a large amount of carbon dioxide, hydrate thereof (carbonic acid) or ammonium, discharging of such targeted water may harm the environment.
Therefore, it is the current situation in the art that there is a demand for a water purifier and water purification method, which can recover purified water by an osmotic pressure while preventing leaks of a volatile solute from an aqueous solution containing the volatile solute into the targeted water, and can efficiently perform purification of water.